IGZO is the abbreviation of indium gallium zinc oxide, and amorphous IGZO is a channel layer material used in the new-generation thin film transistor technology, which is a thin film transistor (TFT) technique and refers to applying a layer of metal oxides on a TFT-LCD active layer. In short, IGZO is just a channel layer material, but not a novel panel technique, and does not belong to the same level with IPS, SVA or OLED. In general, IGZO is still within the scope of TFT-LCD. IGZO material is first proposed and used in the TFT industry by Hideo Hosono, from Tokyo Institute of Technology. IGZO-TFT technology first achieves mass production in Japan Sharp Corporation.
TFT (Thin Film Transistor), which is positioned in pixel driving modules within a lower glass substrate of a liquid crystal panel, is in a form of a thin film, and is embedded in the driving modules together with pixel elements. A TFT liquid crystal screen means each liquid crystal pixel site on the liquid crystal display panel is driven by a thin film transistor integrated thereafter. In general, the features of TFT are essentially the same as those of a semiconductor transistor. A drive current of TFT charges a pixel capacitor, and turns on an electrical converting apparatus of the pixel, while IGZO is used on TFT.
As shown in FIG. 2, when metal is in contact with IGZO, a semiconductor band bends at an interface to form a barrier. The presence of the barrier will lead to a large interface resistance, such that a Schottky diode contact is formed between a source 3 and an IGZO layer 4 and between a drain 4 and the IGZO layer 4. Schottky resistance will cause an on-state current of a TFT element to be in an undercurrent condition, a sub-threshold swing (SS) to be too large, and the stability of the element to be decrease, which will affect the image display quality.
Therefore, an important factor for determining the performance of the semiconductor element is to reduce the contact resistance between metal and IGZO to form Ohmic contact. One of the methods of forming good Ohmic contact is to perform N-type doping (n+IGZO) on a semiconductor region in contact with the metal, such that a depletion region of the interface gets narrowed and electrons have more chances to conduct direct tunneling (Tunneling Effect).
Existing methods of N+IGZO (i.e. N-type doping) utilize doping, namely injecting heavy metals, H+ or others into the IGZO after the completion of IGZO, which is a complex and time-consuming process, and substantially increases manufacturing costs.